For electricians
Safe isolation procedure
The industry-standard sequence for isolating a low-voltage circuit before working on it — aligned with HSE GS38, HSG85, the Electricity at Work Regulations 1989, BS 7671 Chapter 46 and the safe-isolation flowchart in IET Guidance Note 3, as reinforced by NAPIT and NICEIC technical guidance.
The ten-step procedure
Identify the circuit and confirm scope of work
Confirm exactly which circuit(s) must be isolated. Check drawings, circuit charts and existing labelling. If the installation is unfamiliar, treat every conductor as live until proved otherwise.
Seek permission and warn other users
Notify the client / duty holder before removing supply. On commercial or shared premises, follow the site permit-to-work system.
Select the correct point of isolation
Isolate at the device that gives secure, single-point isolation of every live conductor (line and, where applicable, neutral). MCB / RCBO for a final circuit; main switch for the whole installation. A functional switch or plug-and-socket is NOT isolation unless specifically designed for it.
Switch off and lock off
Operate the device to OFF and secure it with a lock-off device and unique padlock. Retain the only key on your person. Where the device cannot be locked, remove and retain the fuse carrier; if that is impossible, place a competent person under continuous supervision at the isolator.
Fit a caution / warning notice
Attach a durable "DANGER — ELECTRICIAN AT WORK — DO NOT SWITCH ON" notice at the point of isolation, with your name, date and contact number.
Prove the voltage indicator on a known source
Before testing the circuit, prove the approved voltage indicator (AVI) on a dedicated proving unit or a known live source. Test L-N, L-E and N-E ranges. GS38-compliant probes only — finger guards, ≤4 mm exposed tip, fused leads.
Test the circuit is dead at the point of work
At the point of work test between: Line–Neutral, Line–Earth, Neutral–Earth, and between all lines on 3-phase. All readings must be effectively zero volts. On TN-C-S be alert to residual voltage from parallel paths.
Re-prove the voltage indicator
Immediately re-prove the AVI on the same known source / proving unit to confirm it did not develop a fault between step 6 and step 7. Only now is the circuit safe to work on.
Carry out the work
Keep the lock-off key in your possession for the entire duration. Do not delegate. If work is paused (breaks, overnight) leave the lock-off in place unless the isolation can be re-established and re-proved on return.
Restore supply in a controlled manner
On completion: inspect, complete any necessary dead tests (continuity, insulation resistance), remove tools and debris, confirm no one is in contact with the circuit, remove the lock-off and warning notice, energise, and carry out live tests (polarity, Zs, RCD). Record on the minor works / EIC.
Minimum kit
- Approved Voltage Indicator to GS38 (e.g. Martindale VI-13800, Kewtech KEWCHECK R2, Fluke T150 — not a multimeter, not a neon screwdriver)
- Dedicated proving unit (e.g. Martindale PD440, Kewtech KEWPROVE 3) — a live socket is a fallback, not best practice
- GS38-compliant test leads and probes: finger guards, insulated, ≤4 mm exposed tip, fused
- Lock-off kit appropriate to the device — MCB clip-on lock, universal MCCB lock, isolator hasp
- Unique padlock with a single key retained by the person carrying out the work
- Durable warning / caution notice with name, date and phone number
- Class 0 insulating gloves and arc-rated PPE where the risk assessment requires it (LV switching on TP boards)
Reference documents
HSE Guidance Note GS38
Electrical test equipment for use on low-voltage electrical systems
HSE HSG85
Electricity at work — safe working practices
HSE HSR25
Memorandum of guidance on the Electricity at Work Regulations 1989 (in particular Reg 12–14)
IET Guidance Note 3 (GN3)
Inspection & Testing — Section 2, safe isolation
BS 7671:2018+A2:2022
Chapter 46 (isolation & switching) and Regulation 132.15
NAPIT / NICEIC codebreakers & technical bulletins
Industry best-practice interpretation of the above
Common failures picked up on assessments
- Using a multimeter or neon screwdriver instead of an approved voltage indicator.
- Proving the AVI on the circuit being isolated — that only tells you the circuit is dead, not that the tester works.
- Isolating at a functional switch (light switch, FCU switch) instead of the circuit protective device.
- No lock-off — a piece of tape or a hand-written note is not isolation.
- Sharing the lock-off key or leaving it in the padlock.
- Forgetting to test N–E on TN-C-S — borrowed neutrals show up here.
- No re-prove of the AVI after the dead test.
- No warning notice, or a notice with no name / date / phone number.